1. Field of the Invention
The present invention relates to a clamp-on type ultrasonic flowmeter apparatus for measuring a flow rate of a fluid flowing through a conduit by transmitting ultrasonic wave beams through the fluid.
2. Related Art Statements
The ultrasonic flowmeter apparatus may be roughly classified into a V-system shown in FIG. 22(a) and a Z-system illustrated in FIG. 22(b). In the V-system, a pair of ultrasonic signal transmission and reception elements a and b are arranged on the same side of a conduit P and an ultrasonic beam B emitted from one of the elements a or b is reflected within the conduit and is received by the other element b or a. In the Z-system, the ultrasonic signal transmission and reception elements are arranged on mutually opposing sides of the conduit 2, and an ultrasonic beam B emitted from one of the elements a or b and propagating across the conduit P is received by the other elements b or a. In both systems, the ultrasonic signal transmission and reception elements a and b are arranged at an upstream position and a downstream position, respectively viewed in a flow of a fluid F flowing through the conduit P. Therefore, there is a difference between a propagating time of the ultrasonic beam B emitted from the upstream element a and received by the downstream element b and a propagating time of the ultrasonic beam B emitted from the downstream element b and received by the upstream element a. A flow speed of the fluid F passing through the conduit P can be calculated from the above mentioned difference in the propagating time, and a flow rate of the fluid F can be obtained by a product of the flow speed and a cross sectional area of the conduit P.
In the following Japanese Patent Publications 1˜3, there are disclosed known clamp-on type ultrasonic flowmeter apparatuses for measuring a flow rate of a fluid flowing through an existing conduit by fitting the apparatus to the conduit from external.